Berg used to be a Senior SEDT (Software Development Engineer in Test) guy at Microsoft and he thinks he has some answers. First up, Berg says one of the major issues is the use of virtualization. These days, most internal tests are performed on virtual machines and no longer on a wide variety of machines.
Internal software testing has largely been replaced by the Windows Insiders program as well as telemetry analysis. Basically, computer enthusiasts and end-users are now doing the work that used to be performed by various Microsoft development teams. Berg says the problem here is that Windows Insiders need to actively report bugs and also be able to document them "expertly".
Berg explains that the internal teams at Microsoft used to be gatekeepers. They prevented the rollout of buggy code to large numbers of users. Nowadays, updates with supposedly small code errors are pushed out to millions of users, which sometimes results in large, unintended consequences.
Via: WinFuture